The present invention relates generally to a melter and applicator for applying filling or sealing material, such as liquefied asphalt, to damaged paved surfaces. More particularly, the present invention relates to a melter and applicator which is able to interchangeably utilize either heated or standard hoses to optimally deliver the filling material.
Paved surfaces are constantly subjected to various thermal and pressure induced stresses. As a result, these surfaces routinely fracture, creating cracking that will propagate if left unchecked, as well as more substantial holes which similarly expand over time. This type of pavement damage reduces the useable lifetime of the surface and also poses a substantial risk to those who utilize it as a means of travel.
Simply tearing up the damaged surface and replacing it in its entirety is far too costly and time consuming to be done on a regular basis. As such, it has become standard practice to repair damaged pavement before it reaches a point where replacement is required. To repair damaged pavement, a section is cut from the surface, which creates a uniform channel. The channel is cut to coincide with the propagation of the cracking and serves to ease the removal of the damaged pavement and any debris which may have accumulated. Once the channel is formed, heated paving material (such as "rubberized" asphalt) that has been liquefied is applied and fills the channel. As the paving material cools and solidifies, it bonds with the surrounding pavement thus sealing and filling the channel. The asphalt provides a flexible joint which effectively seals the crack, preventing water from seeping in as the pavement expands and contracts.
Due to the nature of the material being utilized, specialized equipment is required to store, prepare and apply the liquefied pavement. This equipment must be portable so as to allow it to be taken to the damaged area. As such, it is usually mounted on a frame which is pulled behind a vehicle. The frame includes all of the components necessary to perform the repairs. In general, solidified paving material, such as bricks of asphalt, are placed into a relatively large bin. The bin is then heated to a temperature sufficient to liquefy the material. The bin is constantly agitated to insure uniformity and to prevent the material from cooling and hardening.
The liquefied material is then pumped out of the bin, through a hose, and out of a nozzle where it is controllably directed into the channel cut into the pavement. Handles are placed at or near the nozzle to allow the operator to control the hose, as the temperature of the material would make direct contact hazardous.
Significant problems occur when the liquefied paving material is left in any portion of the system and allowed to cool. Specifically, the various connecting pipes and hoses will become plugged and either seriously impede or totally prevent any subsequent fluid flow. Material left within the pump will also solidify, rendering the pump inoperable. To use the pump again, it must be heated for a relatively long period of time, thereby liquefying the pavement material, and allowing fluid flow through the pump. As such, it becomes necessary for the operator to perform this step well in advance of when the applicator is expected to be used. Therefore, in normal operation, the pump will only be allowed to solidify when the applicator is no longer needed in a given day. The following day, the applicator is then heated prior to its initial use to free the pump and thereby bring the applicator into a working condition.
To avoid such problems, previous melter/applicators have sought to prevent the material from cooling at any point within the system. To accomplish this, the various components are kept at or above a temperature sufficient to maintain the paving material in a liquid state. There have been two separate and distinct methods for accomplishing this. In the first method, a cabinet is provided that is adjacent to the heating chamber and/or the heated bin. The pump is located within this cabinet and is maintained at the proper temperature through the heat transfer that occurs due to the proximity of the cabinet to the heating chamber and/or heated bin. In addition, these melter/applicators always employ a recirculating pump. That is, the pump is either continuously or systematically actuated to draw the liquefied material from the bin, through the pump and then deliver it at least back to the bin. This serves to bring heated material to the pump, which acts to heat the pump and also prevents any of the liquefied material from settling within the pump. When the operator desires to use the applicator, this recirculation is minimized thus directing a majority of the fluid flow through the hose.
The hose itself is a primary area of concern. If left alone, the liquefied material would solidify in a relatively short period of time, either seriously occluding or totally blocking subsequent fluid flow. Generally, when in use this problem is minimized in that heated liquid is constantly flowing through the hose. This serves to both heat the hose and to remove any material which may have congealed. During periods of sporadic use or during periods of non-use, the paving material will have a tendency to solidify. To prevent this from occurring, sufficient room is provided within the cabinet to allow the hose to be stored. While in this heated environment, the paving material is kept at or raised to a temperature above its congealing temperature.
While the heated cabinet can effectively prevent material solidification when properly used, it may be under utilized. That is, the operator may have a tendency to leave the hose out at times when it should have been placed in the heated cabinet. For example, the operator may have underestimated the time between consecutive applications. Due to the bulkiness of the hose and the hassle associated with coiling it into the cabinet, the operator may err on the side of leaving it out, if time is a consideration. Therefore, applicators utilizing a heated cabinet have also provided a wand access port. This allows the operator to place the wand of the hose into the wand access port and to allow the liquefied paving material to flow through the hose and back into the bin. By so doing, the paving material is prevented from solidifying within the hose and the operator is less burdened.
In the second method, the heated cabinet and recirculating pump have been eliminated altogether. Instead, a pump is actually placed within the heated bin and is therefore always maintained at the proper temperature while the applicator is in use. The pump does not continuously recirculate material. However, when material does not flow through the hose during extended periods of non-use a heated hose must be utilized, such as with the mix applicator shown in U.S. Pat. No. 5,832,178, issued to Schave on Nov. 3, 1998. Hoses can be heated by generating an electrical current through a wire (or wires) that is coiled about the outer circumference of the hose. The hose is heated right up to the coupling of the hose to the pump outlet, thus leaving no section of the pump or its couplings unheated. The heated hose can be left unused for relatively long periods of time, as the heating element coiled about the hose will prevent the pavement material from solidifying. Traditionally, a relatively long wand (several feet long) is coupled to the end of the hose. A valve is usually located at this connection, allowing the operator to control the flow of liquid. Since the wand is so long, it must be heated separately. As such, a second electrical heater is wrapped around the wand section, thus preventing material solidification from occurring there.
Substantial problems occur when the pump fails, as it is located within the bin. That is, when a failure occurs, the liquefied material in the bin must be dealt with while simultaneously attempting to service the pump. If the material solidifies, it must be melted in order to gain access to the pump. When the material is liquefied it must then be removed to allow access to the pump, thus seriously complicating an otherwise simple task.
While effective at preventing material solidification, the electrically heated hoses are very expensive (in excess of $2000.00 per hose). Generally, heated hoses will cost 3-5 times more than standard, unheated hoses. A failure of a heated hose results in the applicator being generally out of service until a new heated hose is purchased and/or delivered, as there is no practical way to prevent stagnant material from solidifying in the hose. Because of their expense, it is not feasible to have spare heated hoses on hand, as this would require a substantial investment, which may or may not ever be utilized on any particular day. For example, a particular paving repair company will likely have many applicators which are simultaneously in use at various disparate, separate job sites. It would simply be too costly to have spare electrically heated hoses brought to every one of these job sites. The company may have extra hoses, maintained at a central location. However, it is not practical to have enough to resupply all of the applicators. Furthermore, it takes time, and hence delays use, to retrieve the hose from such a central supply. Such delays of course result in loss of revenues.
The hoses for melter/applicators are made as durable as possible while still allowing sufficient flexibility to perform its repair function. However, the hose for a melter/applicator is exposed to harsh conditions. It is continuously dragged over rough pavement, repeatedly heated and cooled, and forced to carry rather abrasive and chemically reactive material. Therefore, the useful lifetime of such a hose is limited. If the hose itself does not rupture, the heating element of a heated hose can be damaged thus eliminating the system's only means of preventing solidification of the paving material within the hose.
Because of the heating element, heated hoses are less flexible, generally much more fragile, and much more cumbersome to work with than standard hoses. As an example, the presence of the heating element makes the heated hose less maneuverable in use, has a greater minimum bend radius which may prevent coiling inside a heated cabinet without potentially damaging the heated hose and which contributes to faster failure of the hose from fatigue as the result of use. As such, many operators choose not to use heated hoses. During the warmer months, when temperatures reach 60.degree. F. (16.degree. C.) or higher, material can be left inside the hose for 2-3 minute periods without solidification occurring. This is usually sufficient time to allow movement of the hose between applications without returning the wand of the hose to the access port, thus making the less cumbersome, standard hose more appealing to the operator. However, when temperatures fall below 40.degree. F. (4.degree. C.), gelling or solidification occurs rapidly over the length of the unheated hose. The heated hoses readily handle such temperatures. Thus, the operator is more inclined to use heated hoses during those periods, even though less maneuverable and more cumbersome than conventional hoses, because it is not necessary to return the wand of the hose to the access port, making the repair process easier and faster under cool temperature conditions with a heated hose. In order for the operator to have such a choice prior to the present invention, separate incompatible systems must be provided. Companies that do this incur substantial costs; those that do not severely limit their operator's equipment choices.
Therefore, there exists a need to provide a melter/applicator which has the benefits of utilizing a heated hose when operating conditions warrant its use, while also accommodating the use of non-heated hoses when operating conditions permit avoiding the shortcomings of the heated hoses.